Solid particulate products, such as grain, animal feed (barley, corn, wheat, and animal by-products), cereals, cat litter, and other particulate materials are normally converted from bulk material into smaller portions for sale. As part of the packaging process, a bulk quantity of product is placed into a hopper. At the exit end of the hopper is a valve that controls the rate that the product flows out of the hopper. To accurately and efficiently fill units of such products, manufacturing technologies have attempted to allow for continuous monitoring of said products.
A number of methods of measuring a run of continuously flowing solid particulate are currently in use: weighing the entire mechanism, measuring the height of the product, inferring hopper level, based on fill weight, and measuring a batch amount. The first method, of determining product weight is to weigh the entire mechanism, which includes the hopper, the feed mechanism and all of the supporting structure. The first steps are to weigh the empty mechanism without the product, and then to re-weigh the mechanism when filled with the product, the difference being the product weight. The drawbacks of this system reside in the fact that often the weight of the mechanism (hopper, feed mechanism and supporting structure) is many times the weight of the product. In order to ensure accurate measurement, such systems require a very high resolution in order to measure the proportionally very small changes of the overall system, in order to ascertain an accurate measurement of the product weight, whose proportions may be fluctuating greatly with respect to only its own magnitude. This is particularly an issue when low density products such as low density polystyrene balls must be measured.
The second method, measuring the height of the product, employs a level detector to measure the height of a volume of product in a shaped vessel or a hopper. This method is unreliable in the context of certain materials, particularly ones that may be susceptible to clumping, or which may become scattered or which become airborne in significant enough volume, before settling-out. Thus it will be seen that the volume of a particulate material can be difficult to be detect, especially when a low density product is present. Because it does not continuously sit as a settled volume, a low density product has a level detected that a sensor can only recognize for the amount which has fallen out of the air, and therefore may not fully account for the entire amount moving through the system.
The third method, determining hopper level or fill by inferring hopper level based on fill weight, is also flawed. Measurement of weight is normally considered a good method of determining hopper level, since bulk density of a given material usually fairly consistent, and it “integrates” the uneven surface level of the product and does not rely on material characteristics. Notwithstanding the foregoing, level by weight is still considered the most accurate method of solid particle level measurement, albeit the most expensive. Hopper level may also be measured directly by employing a level sensor positioned above the hopper, but this method can be unreliable due to product shape. In addition, the surface characteristics of some materials make it difficult to reliably sense the location of the surface.
The last prior art method measures a batch amount of product delivered to the hopper, in order to make the estimate of the overall system flow rate. Whether by weight or by volume, for a given batch amount, the product of the batch and the time which is required to deliver a batch amount yields the flow rate. A change in weight with respect to time is the flow rate, or in other words, the first derivative of the weight with respect to time yields the flow rate. There are currently two measurement methods or techniques in general use—supported and suspended. Like the first of the discussed prior art methods, ascertaining the loss-in-weight of an entire system, the entire weight of the mechanism (the hopper, vibratory tray and the electromagnetic drive) plus the weight of the product is measured. As a result, even though the analysis focuses upon a different criteria, the apparatus for performing such methods still requires the high resolution weighing systems that bring the disadvantages of unreliability, complexity, inaccuracy, and increased cost.
In view of the foregoing, it is an object of the present invention to overcome the drawbacks and disadvantages of current systems.
Another object of the present invention is to provide a system that weighs only the product and its container to improve measurement accuracy.
Still another object of the present invention is to provide a system to accurately measure product weight or flow rate that is less expensive than similar systems currently in use.
A still further object of the present invention is to provide a system to more accurately measure product weight or flow rate that is more reliable than similar systems currently in use.